DIY: E32 Brake Light Circuit Warning Light Repair

[Legoman]

And of course I spoke too bloody soon didn't I?!?!?!?!? Just had the car throw the bloody Brake LT Circuit warning crap on the dash CCM again!! Arrrgghhhh! I hate this car. Who wants a perfectly good E32 740iL with a completely unsolvable CCM warning module error?? Anybody?? Take it away from me please before I put a GD screwdriver straight through the instruments!

What do you do when your brake lights all work perfectly well, you've replaced all the globes, all the globe holders, the brake switch and resoldered every GD joint on the CCM board along the Green 7 track that serves the Brake LT circuit warning? What else is there to do besides smashing the whole instrument cluster to a million pieces with a sledgehammer?

[shogun]

Try another CCM?

[Legoman]

Try another CCM?

Not possible here. It's not like there are E32 740's growing on trees here. Mine is the only one I know of on this side of the country and all the ones on the other side are in a wrecker's yard.

Is there any truth to a rumour that the electric headlight throw adjuster stepper motors are on the same circuit as the brakes and when they fail, they draw too much power causing the stupid warning message on the dash? There's a guy here suggesting that unplugging the headlight adjuster motors can prevent reoccurrence of the Brake LT Circuit warning. Any truth? - Irrelevant: My car doesn't have motor controlled headlight beam throw adjusters. It has SLS instead. You don't have both because one negates the need for the other.

Failing that, is there any way of permanently modifying the circuit board of the CCM to forevermore disable this circuit from reporting faults to the dashboard? It's not as if I need this circuit warning anyway. The warning is completely and utterly useless since all it says is "look in your owner's manual" and all the owner's manual says is "take the car to your dealer" which is completely and utterly F'kn useless since the dealer here will just diagnose that the car is too old and needs to be replaced with a shiny new one.

[Legoman]

The new attempted solution is to solder in wire bridge links across the top of the PCB tracks to duplicate the paths for the circuit so that if there are any micro-cracks in the PCB tracks that open up just enough in the cold weather to increase the resistance to trigger the warning, then these will be bridged by the extra wires.

This plan is based on a belief that the source of the fault is still within the CCM board itself. A belief based on a significant reduction in the sensitivity and frequency of false positive warnings since the last joint resoldering attempted fix and a continued observation that cold weather is very much a pre-requisite condition to trigger a false positive warning.

[E32FAN]

The new attempted solution is to solder in wire bridge links across the top of the PCB tracks to duplicate the paths for the circuit so that if there are any micro-cracks in the PCB tracks that open up just enough in the cold weather to increase the resistance to trigger the warning, then these will be bridged by the extra wires.

+1 for this fix. The problem is that this board is single-sided, so there are no plated-thru holes. After 20 years, the solder lands become disconnected from the copper traces. The connections can be bridged with wires as you describe.

[Legoman]

The problem is that this board is single-sided, so there are no plated-thru holes. After 20 years, the solder lands become disconnected from the copper traces. The connections can be bridged with wires as you describe.

I'm reliably informed that 20+ years ago single sided boards were normal. Double sided boards were a lot more difficult to produce and *less* reliable as the vias (the conductive plating on the inside of the holes through the board to provide electrical connection from one side to the other) were difficult to do properly. If BMW had used a double sided board of the era, it would have actually failed long ago.

The failure mode is actually from continual vibration in a vehicle causing microscopic cracking in the solder joints. If it hadn't been conformally coated then redoing each solder joint would be a trivial exercise and give it another 20 years of service. But then if it hadn't been conformally coated it probably also would have failed long ago due to corrosion.

All in all given the technical limitations of the time the car was actually built, it was done in the best way possible. So really, this hassle is just my deserved punishment for hanging onto a car for 26 years well past its best-before date.

[G46]

i tried the method, inserted bare wire on pin 7 of ccm, connect to test pen, and the other hand to the positive side of the battery charger post, when i pushed the brake, it doesnt lit up..

VIN is DE25081

[shogun]

found on the website of Zeckenhausen the following: After replacing pads and sensors, the dash warning will still be illuminated. However, you do not need your BMW dealer to reset the warning message. To reset the warning on most pre-iDrive models, turn the ignition key to the run position, but do not start the car. After about one minute, the brake pad warning will reset. For newer models, the technique to reset the warning may vary.

and this I posted years ago: BMW Brake warning light reset (found this on the net: never tested it on my car, but in the general BMW forum some confirmed this after I posted that)
Make sure that you replaced the sensor and the brake pads if you did not replace the sensor or pads this will not work. Turn the key to position two (when all of the inspection lights are lit), leave it in this position and leave your driver’s door open a few seconds (between 15 to 90 seconds depending on your car) and it magically resets. If that did not work turn the key to position two and push down on the brake then turn the key off and check to see if it turns off (door must also be open). If this still does not work press down on your brake (hold it pushed down) and turn the key to position two and wait until it turns off. If none of these work please go back and check that you installed the sensor correctly.

[shogun]

anyone else was successful by this method with the extra current from the test lamp (about 0.3 Amps) to clean the contacts?
If not, how did you solve the brake light circuit warning light problem? Change to new brake light switch? Replace/repair the CCM?

[Legoman]

The current cleaning trick did not work for me, or if it did, then it was so fleeting that it just carboned-up again straight after and the problem resumed. There are apparently two relays on the board that control the current to each of the headlights. One for left, another for right. Why they're controlled independently like that I have no idea, but it may be something to do with the perimeter distance lighting feature turned on with the indicator stalk. Anyway, the only cost effective solution I could come up with was to figure out which one of the two relays was the dodgy one and then isolate it from the circuit and use the remaining one to sevice both headlights simultaneously.

This has significantly reduced the number of warnings coming up, but has not solved the problem completely. I will still get the odd warning every now and then on particularly cold mornings, however, I have learned to live with that for the time being because there seems to be no other sensible long term solution.

[johan750]

Haven't had a lot of time to read forums the last couple of years. So read this too late..just ordered a new brake light switch as the e34 is starting to give this fault. Al tough I think I'm going to give it a go as its easier then getting under the dash :-)

Thanks for posting this Erich!

[Annddrriy]

Do you know if brake light switch cars with EML connect to the TCM pin 26 ? Thanks !

[shogun]

check ETM https://shark.armchair.mb.ca/~dave/BMW/e32/
EML brake light switch has brake light switch and brake light test switch, for part numbers see ETK https://www.europeantransmission.com...MW/EML-BMW.pdf

[Annddrriy]

I did check ETM could not realize the wire blue/red is coming from the brake light switch goes to two modules ABS pin 25 and automatic transmission TCM pin 26 or it should be with in one of the modules or for both ? Thanks in advance for your answer ?